It seems some think Spinks could present problems for Joe Louis, and possible get a decision. So I'm curious then, does he then beat Johnson? It will be ref'd like a fight from 1910, with that rule set, but is only scheduled for 15 rounds.
Over a short distance, probably Spinks. Over the distances Johnson was used to, I think he'd break Spinks down.
To paraphrase Don King, in this fight Spinks has 2 chances, slim and none, and Slim's out of town. I think Spinks as a HW is generally quite overrated by some on here, especially it seems by those who weren't "there at the time". His HW resume basically consists of 5 fights; 1) a win over a creaking long time champion in Holmes, which although looks good in terms of the bald result "Michael Spinks W15 Larry Holmes", was actually against a tired Holmes in is 3rd fight in 6 months and was basically looking for an easy win to equal Marciano's record. 2) a highly questionable decision in the rematch. 3) a win over Steffen Tangstad in poor voluntary defence after Tangstad had previousy been knocked out by Anders Eklund and had swallowed it in both the Eklund and Spinks fights. 4) a win over a washed-up Cooney who apparently had drink & drug issues. 5) Mike Tyson. People will say Spinks beat Holmes & Cooney in defence of Spinks' resume but they were Holmes & Cooney in name only. At the time it seemed to me that Spinks wanted no part of Tony Tucker, Pinklon Thomas, Witherspoon et al. I believe all these would have likelt soundly beaten Michael Spinks as a HW. Jack Johnson, I am sure, would have soundly beaten Michael Spinks, whatever the scheduled distance. Although the shorter the distance the better for Spinks, as his awkwardness could take time to solve. I believe Spinks was a boxer whose "patterns" were harder to read than most.
Johnson doesn't look as good to me on film as his reputation suggests. Skills wise it seems to me Spinks > Johnson. On the other hand you can also see Johnson's style is more suited to long contests and that he's teak-tough both mentally and physically. I don't see JJ quaking at the thought of facing Tyson, for instance. Hence my post.
I think Johnson. Especially with his ruleset, allowing all the tricks that haven't been used in decades. The one thing is if Spinks can keep it long, since he has a bit of height, and footspeed is probably Johnson's weakest area.